EFFECT OF HARVEST DATES ON YIELD AND COMPOSITION OF FORAGE KALE

Abstract

Forage kale (Brassica oleracea L. ’Maris Kestrel’) was sown on 27 May and harvested at 18- to 22-d intervals between 16 Sept. and 6 Dec. in 1985 and 1986. Dry matter accumulated until early November and then declined at about 19 kg ha−1 d−1 until the final harvest. In vitro digestibility of dry matter (IVDDM) ranged from 916 to 952 g kg−1 among harvest dates. Crude protein was similar for most harvest dates. Hemi-cellulose content decreased in 1985 but not in 1986 while cellulose content decreased in 1986 but not in 1985. Lignin content increased from 25 to 43 g kg−1 between mid-September and early December. The cell content peaked at 814 g kg−1 in mid-November. There was an increase in S-methylcysteine sulphoxide (SMCO) concentration of leaves from 1.4 g kg−1 to 6.2 g kg−1 between the first and last harvest dates. Potassium concentrations increased in 1985 and decreased in 1986 from September to December while concentrations of P and S were not influenced by harvest dates. With later harvests, both Ca and Mg concentrations decreased while B decreased in 1985 but not in 1986. Zinc concentrations peaked in October in 1986 while in 1985 they were similar for the five harvest dates. Iron concentrations fluctuated in the two years while Cu and Mn concentrations were not influenced by harvest dates. Forage kale provided highly digestible dry matter in late season. The mineral composition of kale was adequate with the exception of Cu, Mn and Zn which would not satisfy the dietary requirements of ruminants. The SMCO concentrations in kale leaves increased steadily from mid-September to early December but were lower than those concentrations considered deleterious to animal health.Key words: Brassica oleracea L., crude protein, hemicellulose, cellulose, SMCO, macronutrients